Apparatus for speech instruction



Jan- 5, 1954 w. s. HOWELL ET AL APPARATUS FOR SPEECH INSTRUCTION 2 Sheets-Sheet l Filed March 9, 1951 mwN JNVENTORS VV/LL/AM 5. HOWELL l JOHN V [QW/N M ATTOP/VEYS Jam 5, 1954 w. s. HOWELL ETAL 2,664,649

APPARATUS FOR SPEECH INSTRUCTION Filed Maron 9, 1951 2 sheets-sheet 2 A T'ToRA/E Ys m W Q ONK G m w W F Q W DMW Q EH mw V ,V. ,x hw w om S m5 d N www, NP. .M W Si@ Y e OQQQN Patented Jan. 5, 1954 APPARATUS FOR SPEECH INSTRUCTION William S. Howell, Minneapolis, Minn., and John V. Irwin, Madison, Wis., assignors to Regents of the University of Minnesota, Minneapolis, Minn., a corporation of Minnesota Application March 9, 1951, Serial N o. 214,668

8 Claims.

This invention relates to apparatus for use in speech instruction. In the teaching of speaking, one of the problems confronting the instructor is that of teaching the pupil to speak distinctly and forcibly. in most speaking situations, it is essential for the speaker to be able to speak in a suiiiciently loud voice to overcome background noise, as before an audience. Accordingly, for adequate instruction in speech, it is essential that the student be provided with adequate training by means of which he or she will obtain proper speech habits, thus enabling the student to deliver audibly and intelligibly the spoken material, notwithstanding considerable vbackground noise.

In the practical field of speech instruction there has heretofore been available no way for enabling instruction of the student in respect to voice level, except for the student to speak before groups where the student, in effect, practices, the group providing the noise level over -which the student must speak. Obviously, the

student has few opportunities thus to obtain training because of the lack of audiences before whom to make the practice speeches. This method of speech `instruction can be carried out with some success in speech classes where each student in turn takes his place before the group for purposes of delivering the address, the remainder of the class meanwhile serving as the audience and serving to provide the level of background noise over which the student must speak. Another mode of training has been to provide the student with a microphone and amplifying system, together with meters indicating the decibel level of sound strength. The idea `when using such equipment is that the student is able to watch the sound level produced by his spoken voice and thus increase the sound level to a prescribed amount.

The disadvantage when using such modes of instruction has been that the system requires coordination by the student of the sound level `of spoken voice against the sound level indication on the decibel scale, and unless the student continuously givesattention to the. sound level on the decibel scale, it not infrequently happens that the students voice will gradually decrease vide anapparatus for providing a background noise over which the studentmust speak during It is a further object of the invention to provide an apparatus of self-regulatory character productive of a background noise while the student is speaking and over which the student must speak during practice.

It is a further object of the invention to provide an apparatus for voice instruction wherein a background noise is generated, and wherein the background noise is amplified and produced in the presence of the student, together with control apparatus for discontinuance of the background noise when the student's voice level is of suiicient magnitude.

It is another object of the invention to provide an apparatus for speech instruction capable of generating and producing a background noise while the student is speaking, when the studcnts voice level is below a prescribed minimum, but which blanks out the background noise when the student is not speaking at all or when, if speaking, the students voice level is above a prescribed minimum.

Other and further objects of the invention are those inherent in the method and apparatus herein illustrated, described and claimed.

The invention is illustrated with` reference to the drawings in which corresponding numerals refer to the same parts and in which Figures 1A and 1B, combined, are a wiring diagram of a representative apparatus of the instant invention;

Figure 2 is a wiring diagram of the power pack serving the apparatus shown in the wiring diagram of Figures lA-lB.

Referring to the drawings, particularly in Figure 2, there is shown a power pack which furnishes the anode-cathode potential supplies and bias voltage for the various electronic circuits of Figures 1A and 1B. 'I'he power pack is energized through alternating current supply lines L1 and Lz which feed through a fuse I0 and switch Il to the primary winding l2 of a transformer generally designated i3 having a secondary coil generally designated 32. The secondary 32 has terminals Irl and i6 and a center tap l5. Another secondary Il serves the filament cathode of the full wave valve 2B and still another secondary coil I3 provided with a center tap I9 serves the ondary potential across the coil terminals ld and I6 is applied to the anodes 24 and 25 of a twoelement rectifier generally designated 26, yThe 3 cathode 21 of the tube 26 is connected through lines 28, junction 29 and line 30 to one terminal of the filament secondary |1 and through line 3| to the other terminal of the secondary, Accordingly, when the switch I I is closed and the transformer I3 is energized, the alternating current potential produced in the secondary i-'l--IS-I is applied between the heated cathode 21 and the anodes 24 and 25 alternately. The anode circuit from 24 extends through line 38 to terminal I4 of the coil 32, whence the circuit con tinues through one half of the secondary coil to tap I and thence over line 33, junction 34, resistor 35 to ground 36. From anode 25 the circuit extends via line 31 to terminal I6 and thence through the other half of the transformer secondary 32 to the center tap I5 and to ground as previously described. The resultant rectified potential between ground 36 and terminal 29 is applied via line 28 through the filter network consisting ofan inductance 39 and grounded condensers 40 and 4| to the terminal 42 which extends to terminal labeled B-j-(I). From the junction 42 a circuit extends at 43 to the junction 44, whence the circuit extends through resistor 45 and line 46 to the terminal B+(2), this terminal being connected through condenser 41 to the ground 48. From junction 44 a circuit also extends through resistor 50 and through terminal 5| to the junction B-j-(3). Junction 5| is connected through condenser 52 to the ground bus 53. Junction 44 is connected to the ground bus through a resistor 54, the ground bus being grounded at 55. From junction 34 line 5S extends through resistor 51 and junction 58 to the terminal C, which provides bias potential, the junction 58 being connected through a condenser 59 to the ground at 60. The transformer secondary 18, the center point of which is grounded at 6|, provides a low alternating current voltage at the terminals 62 and 63 which serve to supply alternating current potentials to all of the cath- `ode heater filaments, not illustrated, of the thermionic tubes shown in Figures 1A-1B.

The terminal B+ I) in the illustrated modification provides approximately 300 volts D. C.

whereas terminals B+(2) and B+(3) each provide a potential of approximately 200 volts D. C., the two separately filtered terminals being provided for circuit isolation. The terminal C provides a bias potential of approximately -5 volts, with reference to the ground potential 36. Between terminals 62 and 63 there is approximately 6-61/2 Volts alternating current. Obviously, the illustrated potentials may be varied in other specific circuit designs within the purview of the invention.

Referring to the wiring diagram. Figures 1A and 1B, at 10 there is illustrated a gas-filled tube of the thyratron type having heated cathode 1 I, a pair of grids 12 and 13 connected together, and an anode 14. The anode is connected through resistor 15 to junction 16 which in turn is connected through resistor 11 to terminal 18 that is connected by a line, not shown, to the B-I-(2) terminal of the power pack in Figure 2. Junction 16 is connected through a capacitor 19 to junction 80 which is connected through resistor 8| to the ground 82. Junction 80 is connected through junction 83 and line 84 and thence through resistor 85 to junction 86 which is grounded at 81. Junction 86 is connected to the heated cathode 89 of an amplier tube 89, the grid 90 of which is connected to junction 9|, which is in turn connected through a condenser A92 to a variabletap 93- on resistor 35. The anode 4^. 94 of the amplifier tube 89 is connected through junction 95 and condenser 96 and thence via line 91 to junction 98, see diagram IA. Junction 95 (diagram IB adjacent tube 89) is connected through a resistor 99 to the terminal |00 which is connected to the B power supply terminal B|-(2).

The bracket over the thyratron tube 1| and adjacent circuits, labeled I, indicates generally the White noise generator. The designation white noise is used because the operation of the tube 'I0 produces a signal containing a very wide range of frequencies in the audible range, and the signal therefrom is a rm and quite annoying sound having a wide range of audible frequency components. This signal is carried through the amplifier 89 and thence through a two-stage amplifier shown under the bracket II of Figure 1A. The two-stage amplifier includes an amplifier tube |0| having a heated cathode |02 that is connected through a resistor |03 and condenser |04, in parallel, to junction |05, which is grounded at |06. The control grid |01 ofthe tube |6| is connected to the input signal terminal 98, previously mentioned, and the two screen grids |08 of the tube I0| are connected to junction |09 on the circuit of anode ||0. From junction |09 a circuit extends through junction III and resistor II2 to terminal ||3 which is connected to the power supply terminal B|(|). The terminal i I I is connected through a coupling condenser ||4 to the grid terminal |I5 of the second stage amplifier tube I|6 having the control grid II1. The heater cathode IIB of ampliiier ||6 is similarly connected through a resistor II9 and condenser |20, in parallel, to the ground bus |2| which is grounded at |22, it being noted that from junction ||5 on the grid terminal a circuit also extends through the leakage resistor |23 to the same ground bus I2|. One of the screen grids |24 of the amplifier ||6 is internally connected to the cathode IIB. The other screen grid |25 is connected through line |26 to junction |21 which is in turn connected to the B+(I) supply terminal |28. The anode |29 of the tube I I6 is connected to one of the terminals |30 of winding I3| of an impedance matching transformer generally designated |32, the other terminal |33 of said transformer being connected to junction |21. The secondary |35 of the transformer is connected by a pair of lines |36 to the loud speaker at |38. Accordingly, when power is supplied to the circuits, the white noise generator shown under the bracket I generates a sound signal, which is applied through the white noise grid control amplifier 69 shown generally under the bracket LII and thence through line 91 to the two-stage amplifier shown under the bracket II and the output thus amplified is impressed upon the loud speaker |38, thus producing an audible sound. The white noise sound level may be varied conveniently by varying the position of adjustable tap 93 on resistor 95.

The microphone into which the student speaks during training is illustrated generally at |40 and has a pair of output leads |4I|42 connected to terminals |43 and |44 of resistor |45, the terminal |44 being grounded at |46. The microphone input is carried to a preamplifier shown generally under the bracket 1V, the preamplifier consisting of a single stage thermionic amplifier tube generally designated |48. The tube |48 has an indirectly heated cathode |49 which is connected through resistor |50 and condenser |5I in parallel to ground bus |52, which is grounded at |53, the ground bus being also connected through condenser |54 to one of the grids |56 of the tube. On the lead of grid |55 there is provided terminal |51 which is connected through the resistor |58 and junction |5 to the )B4-(3) terminal |60, the terminal |59 being in turn connected through resistor |ii| to terminal it on the anode line |63 connected to the anode it@ of the amplier tube. Control grid It of the amplier is connected to the input terminal M3 from the microphone. The voice signalproduced in the microphone Idil is accordingly ampliiied and the alternating current component of it is transferred by a condenser |70 which is connected to terminal |82 and to the terminal ill. rShe terminal is connected through a resistor |2, which is grounded at lis. The resistor l'! 2 is provided with an adjustable tap |24 so that a portion of the amplified voice signal can thereby be impressed upon the control grid |26 of an amplier tube generally designated Ill which forms a part of the white noise control circuit shown generally under the bracket designated l?.

The white noise control circuit V includes the tube Ill which is not only an ampliiier but also has a pair of anodes adjacent the cathode thereof for the purpose of rectification as will be explained. The tube lll has an indirectly heated cathode V58 which is connected through a resistor |19 and a condenser |89 to the ground bus lei which is grounded at |82, the ground bus being connected also through the condenser |83 to the terminal |813 of the lead extending from the grid .|85 of the tube li'i. The anode-|86 of the tube |17 is connected through line |81 to junction its which is in turn connected through the resistor |39 to the terminal ist which is connected to the input post |9| that is in turn connected to the B power supply terminal B-l-(3). The terminal |90 is also connected through resistor |92 to junction |313.

Junction |88 is connected through a condenser |93 to junction |9d which is connected back through the line |95 to a pair of anodes |96 situated within the tube and adjacent the heated cathode |l8. The junction |9| is connected through junction |97 and then through resistor |98 and junction |99 and thence through resistor itil-and junction 20|, resistor 262, to line 293 which is connected to junction 98 of the grid lead of amplifier tu'be lill of the amplier shown under the bracket II. From junction I9?, previously mentioned, a circuit extends through resistor Zd to ground bus 205. Likewise, from junctions |99, and 20| circuits extend through condensers 296 and gill, respectively, to the same ground bus 25, the ground bus being grounded at 2%.

Assuming that the white noise generator shown under the bracket I is operating as previously described and that the signal thereby generated is transferred through line 8d, variable control resistor Sii-s3, the white noise grid control ampliiier III (tube B) thence through line 91 and through the two-stage amplifier under the bracket II to the loud speaker |38, such noise signal will be impressed upon the loudspeaker 53S and produce a loud noise. If under such circumstances the students voice waves are impressed upon the microphone i :til the voice signal thereby produced will be transferred through the condenser llil and through the variable resistor IlZ-llfi to the grid of tube |71 of the white noise control circuit V. The output of tube |11 is an alternating current Waveat |83 which is impressed through the condenser |93 upon the terminal |965, only the alternating current component of the signal |88 being thus impressed at terminal me. This alternating current component is rectified by virtue of the connection back to line |95 to the rectifying anodes |95 which are in rectiiying relationship to the cathode |18 of the tubes Ill and accordingly a rectified potential builds up through the network composed of resistors 2510 and 262 and isltered by virtue of resistor 204 and capacitors 205 and 201 so that as a result a negative D. C. voltage component will appear on line 203 which may be as much as 40 or 50 volts negative. Such rectiiied component causesv the entire circuit consisting of line 2|i3, junction 93 and line 9i, as Well as grid |01 of the tube il to become suiiciently negative so that the tube is biased to non-conductive condition, and accordingly the white noise signal whch is impressed as previously described through line 9? upon the grid of tube lill, produces no conductivity in tube |0|, even though some such signal may still be impressed upon such circuit in normal strength. This is due to the negative condition of line 203.

The degree to which the line 203 is made negative depends upon the strength of the voice signal produced at microphone |40, and the effective portion of the voice signal, which is varied by adjustment of the resistor |'|2-|'|4. Accordingly, once the resistor |72-.|`|4 is adjusted there is thus established a predetermined circuit setting and the value of voice signal produced by the speakers voice must be suiiicient sothat the selected portion thereof (resistor V12-|74). when amplified and rectiiied will produce requisite negative condition of line 203 and hence of grid itil to render tube |0| non-conductive. By thus speaking sufficiently loud, the speaker blanks out the white noise. However, if the speakers voice is not loud enough, the negative bias at line 203 is less negative and hence the white noise sound is produced at the loud speaker |38. Therefore, the student is provided with a distinct audible prodding whenever the students voice decreases below a prescribed level and the student is thereby instantly reminded to increase the voice level. This accomplishes a distinct value in teaching the student to maintain suii'icient voice level.

In the system thus far described, when no voice signal is produced by the microphone |40, a white noise signal is produced at the loud speaker |38 and accordingly when the student pauses, as he shouid and m-ust for effective speaking, the white noise is instantly reproduced during and continuously throughout such pause. It is perfectly possible to use the instrument in such condition, although the white noise thus produced during the pauses is slightly annoying. The student, however, can become accustomed to this condition of operation of the instrument, and the instrument therefore-serves a useful function eve with this mode of operation. f

However, for preferred results it is desirable t suppress the white noise during those natural and desirable pauses which may properly occur during any speech. For this purpose-there is provided a control arrangement shown within the box outlined with dotted lines and extending partly in Figure 1A and partly in Figure 1B, the box being denoted by the corners A-BC-D. Within the box there are two main circuit components, a

squelch circuit. shown generally under thev bracket VI' and a squelch release circuit which has a portionover the bracket VII in Figure 1A resistor 2li id oohhooted'to one aide.' ofa tr ier oohdeiioer 2 i5 to which i'eforehoe will here .r

be Kehoe dhd ihe other .hd oi .the resi eiodhded ai. .2id- The 'siehe/1 Whioh .Sthe potential o f grid 2i2 ris selected Yaryng the position of Variable A tz-p l213 on the resistor ZI. The anode 218 o f tube 2 I0 isoonnected to junction 2|9 which is in turn onnectedthrough'resistor `22.0 to the terminal 22.! ihdiis .eohhooied to the B oohhir torhiihel B+ 2g Jiiho 'oh'2'l`9' is 4oohheoied through oohdehoe'r .2.22 to' iiilioiioh z2`23'2-hfi beopen or vclosed manually, land .through a filter .circuit extending frorn Yjunirtion 225 throllhwresistor 226 and junction .22.1 v.and resistor 2,23 .and `iunction 229 to lineV 123), which turnclnnested to the junction Si on the grid leadof grid 90 of the white noise control ampliervIII, previousiymehiiohodl .From the' ihheiion' .22.5 .oh .the lter circuit, a circuit ete'nds'througli resistor23l .to the 10.115.232 Likewise, i.iohi'iuiihiiohdZZ-'l .hd 22 9, circuits .extend throughcondensers 2.33 and 213,45, respectively, tothe bus 2,32. The bus 2?'2- is connected to the terrninal 236 .which isdn turn oohheoied io the -5 Yoh lC hier i'ehiihei .of the power supply show Figure 2. From iehmihfi 22:. it rillhofhoied their y...oirohii ehiohdo Vio .line-1.24.0 oh Fiehreiheh, hehoe through the dome @denominar non... 24.0 .ohhieoho .1A to aoehode .2419i e To Ihhhod amplifier dhd rehiiher-tube-seherally deoiehated 242.. The iuhe-242 has-.e .odihoder which-.is indiieoti-y heated ahd .is .oohheotod throheh e resistor .244 and condensed@ innere-.11.121 .to the ground bus 246 .which .is oohhooted through ground .Junction :25.8 to :ground 25.5- -irom lthe ground bus a .oiroiiit-elso extendo :through .ooh- .denser .2.59 .to terminal y.25| on .the Yleado .arid y252 of tubegd. .from .groundtermnal 24.8 a circuitextends through resistor 2.5;3 and ,thence through aline 2.54 lto .terminali 'H @Hondenscr |10 .previously described. :From theyariebleftapqz Supply .terminal/.of the .p0w.e.r .pack shown in :Eigvure 2. Fromthe-iunetionsl onthezleedoigrid 2.52 of tube 242 a 1circuit-..extern is through-resistor 26S to the B power Supplytelmndlfl- "The-sisfda-1 rat iS transferred lrafcounling .cond heer est to the terminalrzjwlhich is,connected3ui 121e .to .another .rectifying anode 121| .adjacent .the .cathode 243 of-ztubetiil. --From the junction Y1.5i] ,a

line

.lter circuit extendsoviaresistorgz, J'unctorrfl, .resistor 2id, junctionf2s15, resistent-'i6 `and junction 2:71 tol .line 213 .upon which a .lterediDaQ .potential appears, .under vcertein..conditions -,of ...operationof thecircuit, .as hereinafter described. -"Ehefilter circuitalso includes a pairof condensers i219tand*2imconnected:inparallelitoethe junctions f.2.13and 2`l5, respectively, -andazresistoreii con- .heotgd .to the ilihotioh 211. .One lside o f eheh of the oohdohoord '2'ih2'ig0 "and resistono l 'dieoorinected together at `junction 282'which is virl turn .connectedl to 5 Volt C bis terminal .283 of the power deeply ohowh ih Fieored- The line 42181, upon whicha negative control voltage appears under certain conditions of opera n, .extend frorn Eigure'l'A to'Figure 1B and is connected to terminal 28:5 that extends through Vthe coupling condenser 2'86v tov terminal 83y previously mentioned, of white noise generator I. The terminal ggfl'ralso connected to the control grid 2g? of amplier 2,9%] in the fs'quelch releasecircuit shown generally under portion VII of 'Figure 1B. The ampiiiier 29? ihoihdeo' dii irdirectly nested catlgloole 253i and an anode .which is .connected .through iiihoiioh .28.3. .io oho Sidoof ihe ooi'ihlihe oohdehoer :2 lo urei/iohoir meriiiohe'd. ihe iuhoiioh 293 being connected through aresistorl 294 tothe termihaizeh which io Served hr the Powe? Siphh' terminal Bei-(7.2) of the power pack shown in .Figure 2. If it is assumed for the moment that the potentialof grid. 213.3 of the v.s'quelch release 'control tube .2.8.9 has e ohiiioiohilr hieh roiioee so that the tube- .239 is conducting, it will then follow that Vthe signal produced by .the whitenoise generator shown under the bracket I and transferred by the coupling condenserZS .tothe grid 2.81 .will .cause an .output atthe anode 292 of .the tube 290 shown .ii-.nder the brdohoiVlI of .Figure 1B- The output voltage of anode 292"is of nixed frequency alter-natirig `trol-tage of .the 4lWhite noise signal, together with a current component. The alternatingcurlent ooponent of such signfl is transferred fria' r.the oooh-line Condenser 215 to the .resistor 2id aV 'portionV of such signal is V,thereby impressecl 'upon the grid 2 i2 of the tube 2130, .which'acc'crdingly liietvise becomes conductiyeandproduces-anainplied signal of the same character' at' its anode terminal '219. The signal .at 21,? `therefore consists of alternating components ,o 'fwary gfreqfienc corresponding .to the fs al igener-fated bythe white noise generator I, 1togetheriu.t`l1' 'a .direct current component.' `Suc`h vfrecfu'encyl alternating .voltage signal is transferredlvia the coupling condenser 222 to the d H 2123." If `it is V.assumed that the vswitch -.2 sed, such signal Iis rectified due A.to the 50 connenct-ilon tialine Zitto therectifying anode 24| I he ube 2542, ,see Figure llA, vover the .bracket 'IhLi-fhus rectied sienalrt terminal 223 is it red y'the network Z5-1.2.3.4 and there .ep-

ars., .terninal 225e. srnooth, negative D C. lv signaLthewLalue ofwhieh nthenegative d portional tothejwhitenoisejsignal input. dhisiouiohi@terminal-12129.moy .he-Ledjusted in nagnitude 'by vr rying the setting of' the `variable.-.tap .2l'3lon .resistor 2 i4 Eand is radjusted to e velue..s.ugiiioieoi Siiohfihiit the fiiigaiive Signal .at y,terminal 229,as .impressed through line 233 Aand.=iuihetioli' d! .upon thegridfd, holds the grid 9D lsuiiiciently .negatiye 4so .that .the tube z89 does not conduct. -Accordingly, thecirCuitr components o .under the brackets gVIandfVI ,of Figure .1B .serve lto interrupt .oivf'squelch .the operrtionV of )the ,control ampliier tube under the bracket III in `Eigure 1B, .andtherefore no usable signal ispro- ,ducedrat the output of .tube B9 under the bracket V*l1-Il andhencethewhite Anoise does notappear at vthe loud .speaker las.

@Such operation, however, depends lupon `the -voltage l:applied to .the .control .grid 281 .of the tubefizishowniunder the lorhoket :VII of. Eighth 9.,. 290 Vno longer conducts and this decreases or interrupts the operation'of tube 20| and accordingly the negative output at terminal 229 is less negative and when sufficiently less negative the tube 8S again becomes conductive. The voltage condition of the grid 251 is hence a controlling condition and such voltage is determined by the squelch release circuit shown adjacent the bracket V of Figures 1A and 1B. This circuit has a signal input which is the amplified Voice component from microphone |45, this signal input voltage being impressed upon the resistor 253 and a selected portion thereof impressed upon the control grid 255 of the tube 242. Accordingly, when the student speaks into the microphone 43 and produces a voice signal, a portion of the amplied voice signal, the amount of which may be varied either by speaking or by selecting a varying resistor 253, is impressed upon the grid 25e of theA grid 242. When the tube 2li? conducts, it produces at its anode terminal 262' an amplied signal of a voice signal frequency, together with .a D. C. component. The voice frequency component is transferred by coupling condenser 268 to terminal 255 and such alternating current voice frequencies are rectiiied kby virtue of the connection to the rectifying anode 21| within the tube 242. The rectified voice frequencies thus at terminal 269 are iltered via the networkbetween junctions 259, 211 and 282, and the filtered rectied voice frequency output accordingly appears at terminal 211 and isimpressed by a line 21S upon junction 285, which is the terminal of the control grid 25? of tube 29e in Figure 1B. The greater the voice signal the more negative will become the rectified filtered,output` at terminals 211, line 218 and junction 255, which is impressed upon the grid 2??.` Tl'ierefore, when the speaker speaks in a suihciently loud voice, a large negative signal will be produced at grid 281 and accordingly tube 2te does not then conduct, with the result that the white noise signal does not transfer through the'tubes 29B and' 2|@ and theltered rectiiied output thereof does not become available at terminals 225 and hence tube 89 of controlamplier Ell does Vconduct the white noise signal which is impressed from junction 23 via line 85, control resistor 55--23 andthen through tube 59 upon line .91 and this signal is accordingly impressed upon the line 91 connected to control grid itil ofthe tube IBI.

It might be supposed that this is justthe converse of the operation desired, but it will be remembered that while the speaker speaks in a suiiiciently loud voice, the white noise control circuit shown under .the bracket V of Figure 1A under such conditions does produce a large negative voltage-output at line 253 and such negative yoltage output pulls the grid M31 of the tube itl (under amplifier II, Figure 1A) suiiiciently negative so that the tube lul does not conduct, regardless of the white noise signals which may 'be impressed thereon. through line 31. Therefore, so long as the. student is speaking suffi- -ciently loudly, no sound is produced at the loud speaker 38.

. Howe-ver, inthe event the student stops speakingentirelnthe voice signal which is impressed upon tube .252 over bracket VH, Figure 1A, accordingly does not exist, and junction 21'?v of the filter network becomes'more positive `,with `the 'result that the white noise 'signal at ses is permittedto be impressed upongrid281 so as to cause tube "290;150 become` conductive. When this occurs tube 2 l also becomes conductive and the resultant signal, which is rectied through the lter network between junctions 225, 229 and 23B is the motivating factor by which the grid e@ of the tube 89 is caused to become more negative, thus causing tube 89 to become nonconductive. Consequently, whenV the student does not speak at all, the loud speaker does not produce any sound. v

However, it may be assumed that there is a middle condition when the student is speaking but not sufficiently loudly enough. When this occurs the amplified microphone output which is amplied through tube |11 (under bracket V of Figure 1A) produces a rectied filtered, negative signal at lineiic, but such signal is not so greatly negative as previously mentioned. At the saine time thelesser amplied microphone signal impressed upon the tube 242 (of network VII, Figure 1A) likewise produces a lesser negative ltered output at terminal 211 and tube 29B may or may not conduct, depending upon how much negative the terminal 211 may be. The amount that such signal is negative is determinedin final analysis by the adjustment of the resistor 253-255, Figure 1A. Accordingly, the instrument may be adjusted by speaking in a low volume and gradually adjusting the resistor 253--255 until at such low volume the white noise signal output is heard through the loudspeaker 138.` The setting of the resistor 253-2 54 accordingly determines the minimum voice loudness below which the white noise will be heardover the loud speaker. When the students speaking voice drops below this minimumthe loudspeaker emits the white noise signal, thus instantly re-` minding the student to speak in a louder voice. When the student does thus speak up the network V interrupts the white noise signal produced at the microphone. y j

In utilizing the apparatusthe following adjustrnents are made: I

After the instrument is warmed up by` turning on power; thefmicrophone is put down so that it will be quiet and the rheostat ZIB-42M, shown in Figure 1B between tubes 299 and 2|0, is then adjusted until the white noise disappears. This adjustment permits theV circuit to operate s o as to obliterate the whiteA noise signal when there is no microphone signal. Next the microphone is placed in operative position and the student speaks into the microphone in low; volume and while vso speaking the rheostat 253-255 (adjacent tube F242 in yFigure 1A) is adjusted until the `White' noise just reappears at the loud vspeaker l33. Then while speaking in a full voice the rheostat i12- 114 is varied as desired'. The Y rheostat i12-|14, for practical operation, is the only control that needs adjustment. This rheostat determines how loud the student must talk in order to overcome the white noise produced at the loudspeaker |33. i l f When' switch 222, Figure iB, is opened, the rst described operation'will ensue, that is to say the White noise control circuit shown under the bracket V will obliterate the white noise whenever the student speaks in a sufficiently loud voice, but when thestudent is not speaking the White noise will reappear at the loud Vspeaker i323, as during pauses. When the switch 224 is closed and there is no voice sound into the microphone les with the adjustmentas previously made, there is no white noise at the loud speaker |38. When the student speaks, butspeaks in too low a tone, white noise will appear at the loud 1'1 speaker |38, but when the' student speaks and speaks above a predetermined loudness, the white noise is suppressed.

The tubes ITI and 242 are combination tubes in which rectifying anodes |96 of 'tube lll and 2li-24! of tube 252 are included. V'If desired, separate rectifying tubes may be provided.

For purposes of ready nomenclature in some of the claims the white noise amplifier III is called the first amplifier; the preamplifier IV is called the second amplifier; the squelch release network VI is called the first bias; the white noise control network V is called the second bias; the tube squelch release network over bracket VI in Figure 1 is called the third bias; tube 89 is called the first valve and tube 290 is called the second valve.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein.

What we claim is:

1. An apparatus for teaching speech compris'- ing electronic means 'for generating a noise sig-` nal of mixed frequencies in the audio rance, amplifying means connected thereto and sound re producer means connected to the' amplifying means for producing an audible noise correspending to said noise signal, a microphone, means connected to the microphone and responsive to the level of signal produced by said microphone for forming a biasing signal, the level of which varies with the level of signal from said microphone, said means for producing a biasingr signal being connected to said amplifier for biasing said amplifier to minimum output when the microphone signal Vexceeds a predetermined amount and for relieving said bias of said amplifier when the microphone signal does not exceed said minimum amount. A

2. An apparatus for instruction in speaking comprising velectronic tube means for generating a noise signal of mixed frequencies in the audio range, an amplifier connected thereto for ampliv fying said noise sien-al, a sound reproduced connected to the amplifier for producing a sound corresponding to said noise signal, a microphone, another ampliiier means connected to said microphone for producing an amplified voice signal when the microphone is operated, a rectifyingfilter network connected to the second mentioned amplifier for producing a bias voltage, the magnitude of which is proportional to the magnitude of said voice signal, said biasing signal being connected to the first mentioned amplifier Vfor biasing said amplifier to minimum output when the microphone signal exceeds a predetermined amount and 'for permitting operation of said first mentioned amplifier and the production of noise sounds in the audio range when vsaid microphone signal is below said predetermined amount.

3. An `apparatus for instruction in speaking comprising means including a source of mixed frequency for generating an electrical signal 4Vin the audio range, a first amplifier connected-thereto for amplifying said signal, a speaker connected to said Erst amplifier for producing a noise signal corresponding to audio-range signal, a rst signal suppression network also connected to said source oi mixed frequency signals for producing a bias signal, Said network being connected to' said amplifyingr means for normally suppressing operation of 'said amplifier, a microphone for producing a voice frequency signal,

a second network connected to said microphone for 'producing another bias signal for suppressing production of said noise signal when the microphone voice frequency signal exceeds a predetermined amount, a third network connected to said microphone for producing a biasing signal when said microphone is operated to produce a voice frequency signal, said third network being connected to the first network for suppressing the biasing function of the first network when said microphone produces said voice frequency Signal.

4. The apparatus of claim 3 further characterized in 'that each of said networks comprises a thermionic tube for amplifying the signal imposed thereon, a rectifier for rectifying said signal, a filter network for smoothing the thus rectified signal.

5. apparatus for speech instruction comprising thyratron thermionic means for generating a noise signal in the audio range, a rst grid control thermionic valve connected thereto for valving the transmission of said signal, amplifier means connected to `said valve and a sound reproducer connected to said amplifier means, a second thermionic valve also connected to said generator and a first bias voltage network having an output connected to the rst thermionic valve for normally biasing said valve to nonconductin'g condition, a microphone having an amplifier connected thereto for producing amplified voice frequency signals, a second bias network connected to said amplifier for producing a second bias signal proportional to said voice frequency signal, said second bias network being connected to said' amplifier for suppressing the operation of said amplifier when the voice frequency signal exceeds a predetermined amount, a third bias network connected to said microphone amplifier for producing a third bias signal when lsaid microphone produces a voice frequency signal exceeding a minimum amount, said third bias network being connected to the second valve for interrupting the operation of the first bias network when said voice frequency signal exceeds a minimum amount.

6. An apparatus for use in the instruction of speaking comprising a thermionio generator of noise signal, a first thermionic grid control valve connected thereto for interrupting the transmission of said noise signal, a first amplifier connected to said valve for amplifying said noise signal when'said noise signal is transmitted and a sound reproducer connected to the first amplifier for producing a noise lsound responsive to such noise signal when the signal is transmitted, a second grid control thermionic valve and a first bias network connected thereto for producing a negative bias when said second valve is conducting, said vfirst bias network being connected to the grid 'of the first valve for biasing said valve to nonrconductin'g Ycondition when said second valve vis in conducting condition, a microphone for generating a voice frequency signal, a second ampliiier connected to said microphone for arn- 'plifying the voice frequency signal, a second bias network connected to said amplier for producing a second `bias signal when the amplified voice signal exceeds a predetermined amount, said sec- 'ond bias 'network being connected to the first amplifier for 'interrupting vthe operation of said first amplier when saidvoice signal exceeds -a predetermined amount, a'tliird bias network connected to said second amplifier for producing a third bias, *said `thirdbias network 'being con- 13 nected to the grid of the second valve for interrupting conductivity of said second valve, after the amplified voice signal has exceeded a predetermined lower minimum value.

7. The apparatus of claim 6 further characterized in that each of said bias networks comprises a grid control thermionic tube having the output thereof coupled by a capacitance to a network, said network including a smoothing circuit and a rectifier.

8. The apparatus of claim 6 further characterized in that said first amplier is a two-stage amplier, the rst stage of which is grid con- 14 trolled and has the grid connected to the output of the second bias network.

WILLIAM S. HOWELL. JOHN V. IRWIN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,194,559 Koch Mar. 26, 1940 2,392,218 Anderson Jan. 1, 1946 2,501,327 Good Mar. 21, 1950 

